1. Field of the Invention
The present invention relates to a light-emitting diode (hereinafter, LED) of side-emission type, and a backlight unit using this LED.
2. Description of Related Art
Among generally known LEDs intended for a light source used in a backlight unit is a side-emission type LED in which an LED element is mounted on a substrate, a reflecting frame is disposed on the substrate and surrounds a peripheral edge surfaces of this LED element, and this frame has an opening which emit light from the LED element toward a peripheral edge surface of a light guiding plate (for example, see Japanese Patent Application Laid-Open No. 2005-223082, p. 3-4, FIG. 1).
FIG. 9 is a perspective view showing an LED for use as a conventional backlight source. In FIG. 9, the numeral 50 represents an LED of side-emission type. The numeral 52 represents a substrate, 53a and 53b represent a pair of electrodes formed on the substrate 52, 54 represents an LED element, 55 represents a light-transmitting resin, 56 represents a reflecting frame, and 59 represents a wiring pattern disposed on a motherboard on which the LED 50 is to be mounted.
The LED element 54 is mounted on an upper surface of the substrate 52, which is provided with the electrodes 53a and 53b and a die-bonding portion 53c extended from the electrode 53a. The LED element 54 is electrically connected to the substrate 52 and sealed by a light-transmitting resin 55. A frame 56 of U shape is disposed on the peripheral edge surface of the light-transmitting resin 55, and an inner surface 56a, 56b, and 56c of the frame 56 are configured to be reflecting surfaces by metal plating, for example. Surrounded by the frame 56, and sealed with the light-transmitting resin 55, the LED element is configured to emit light through a light emission surface 55a, which is an opening of the frame and exposes a portion of the peripheral edge surface of the light-transmitting resin 55.
An anode and a cathode electrodes of the LED element 54 are electrically connected to the electrodes 53a and 53b at disposed respective ends of the substrate 52 by die bonding and wire bonding. Both the electrodes 53a and 53b are in electrical connection with the wiring pattern 59 of the motherboard.
In other words, the conventional LED 50 has an LED structure in which the light emitted from the LED element 54, which is mounted on the substrate 52, is reflected by the inner surface 56a, 56b, and 56c of the frame, and emitted outside through the light emission surface 55a with high efficiency.
However, in the conventional LED 50, the LED element 54 is mounted on the substrate 52, and the bonding wire is further extended from the upper surface of the LED element 54. The LED 50 therefore has a predetermined thickness, which gives rise to the following problems.
FIG. 10 is a partially sectional view showing the physical relationship between the conventional LED 50 and a light guiding plate 60. The thickness of the substrate 52 and the total thickness of the LED 50 will be designated by the numerals 61 and 64, respectively. A peripheral edge surface of the light guiding plate 60 facing the light emission surface 55a receives light emitted from the LED element 54.
Since the LED element 54 is mounted on the substrate 52, the center of the emitted light 65 from the LED element 54 is raised by an amount which accords with the thickness of the substrate 52. There has thus been a problem that a thickness of the light guiding plate 60 has to be large in accordance with a thickness of the substrate.
Since the center of the irradiation light 65 is raised by an amount which accords with the thickness of the substrate 52, there has been another problem that the amount of irradiation light drops in the lower part of the light guiding plate 60.